Kenwood TK-5310 K4 Service Manual page 18

TK-5310
If an optional scrambler board is installed, the switch
(Q454) adjusts the signal path so that the audio signal is input
to the CODEC through the scrambler board.
If the optional VGS-1 (Voice Guide & Storage unit) is
installed, the switch (IC450) will adjust the signal path so that
the audio signal from the microphone is output to the VGS-1
and the audio signal from the VGS-1 is input th the CODEC.
The audio signal is input to the CODEC (base band circuit)
through the above path.
4-2. Base Band Circuit
The base band circuit of the transmitter system consists
of the following:
• CODEC (IC454)
• DSP (IC8)
• LPF (IC456)
• Buffer (IC459)
• DAC (IC462)
• Amplifier (IC463)
The audio signal output from the base band circuit is
converted to digital data of a sampling frequency of 48 kHz
and a quantization resolution of 16 bits by the CODEC
(IC454). This digital data is sent to the DSP (IC8), and voice
signals of 300 Hz or lower and frequencies of 3 kHz or higher
are cut off and an audio range 300 Hz to 3 kHz is extracted.
The audio signal is then pre-emphasized in FM mode and
synthesized with the signals, such as QT and DQT, as
required, and is then output from the CODEC. In P25 mode,
the audio signal is converted to the C4FM base band signal
and output from the CODEC. The DTMF and MSK base band
signals are also generated by the DSP and output by the
CODEC.
LPF (IC456) removes quantization noise from the base
band signal output from the CODEC.
The buffer (IC459) sets the base band signal level to the
DAC input range.
The DAC (IC462) assigns the base band signal to the VCO
(Q107) and VCXO (X100).
At this time, the level output according to the transmit
carrier is fine-adjusted according to the modulation method
of FM Wide, FM Narrow and P25.
EXT.MIC
MIC(MAIN)
MIC(SUB)
MSW/CTS
MM
18
CIRCUIT DESCRIPTION
D450,D451
DET
IC705 MIC
Q455 Q452
AGC-AMP
SW SW
IC452
LPF
N/C
AMP
IC450
SW
VGS-1 VATS
Fig. 6 Audio band and Base band circuit
4-3. Transmit Signal Amplification Circuit
(From T/R switch to Final amplifier)
The transmit signal passing through the T/R switch
(D200) is amplified to approx. 50 mW by the two transistor
amplification circuits (Q200, Q210). The transmit signal
output from Q210 passes through an attenuator to improve
high-frequency signal matching is amplified by the drive
amplifier (Q202) and applied to the final amplifier (Q205). The
signal applied to the final amplifier is amplified by the final
amplifier so that the antenna output is 4 W (1 W for Low
Power).
4-4. High-Frequency Signal Switch Circuit
(From Antenna switch to ANT output)
The transmit signal output from the final amplifier (Q205)
passes through the antenna switch (D202, D203) and LPF,
and goes into the SPDT switch (IC202, IC203) which changes
the antenna connector (CN204) and the universal connector
(CN205).
The transmit signal passing through the output change
switch passes through the surge protection HPF and
spurious removing LPF and then goes to the antenna
connector (CN204) or the universal connector (CN205),
specified by the SPDT switch (IC202, IC203).
4-5. APC Circuit
The APC circuit detects the current of the drive amplifier
(Q202) and final amplifier (Q204) during transmission and
controls the output power by controlling the current.
It detects the current using R220 and R222 and applies a
drop voltage between both resistors during transmission to
APC (IC201). It controls the transmission current of the drive
amplifier and final amplifier so that it is constant by
comparing this current with the reference voltage output
from pin 7 of IC200. The reference voltage input to pin 5 of
IC200 is output from the DAC (IC462). High/Low power
output is set according to the DAC output voltage.
Scrambler board
IC462
Q454 IC8
DAC
SW DSP
IC454 IC456 IC459
CODEC LPF BUFF
SCSW
Q107
VCO
IC463 X100
AMP VCXO